/*
 * Copyright 2002-2010 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.util;

import java.util.Arrays;
import java.util.Collection;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Properties;

/**
 * Miscellaneous collection utility methods.
 * Mainly for internal use within the framework.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @since 1.1.3
 */
public abstract class CollectionUtils {

   /**
    * Return <code>true</code> if the supplied Collection is <code>null</code>
    * or empty. Otherwise, return <code>false</code>.
    * @param collection the Collection to check
    * @return whether the given Collection is empty
    */
   public static boolean isEmpty(Collection collection) {
      return (collection == null || collection.isEmpty());
   }

   /**
    * Return <code>true</code> if the supplied Map is <code>null</code>
    * or empty. Otherwise, return <code>false</code>.
    * @param map the Map to check
    * @return whether the given Map is empty
    */
   public static boolean isEmpty(Map map) {
      return (map == null || map.isEmpty());
   }

   /**
    * Convert the supplied array into a List. A primitive array gets
    * converted into a List of the appropriate wrapper type.
    * <p>A <code>null</code> source value will be converted to an
    * empty List.
    * @param source the (potentially primitive) array
    * @return the converted List result
    * @see ObjectUtils#toObjectArray(Object)
    */
   public static List arrayToList(Object source) {
      return Arrays.asList(ObjectUtils.toObjectArray(source));
   }

   /**
    * Merge the given array into the given Collection.
    * @param array the array to merge (may be <code>null</code>)
    * @param collection the target Collection to merge the array into
    */
   @SuppressWarnings("unchecked")
   public static void mergeArrayIntoCollection(Object array, Collection collection) {
      if (collection == null) {
         throw new IllegalArgumentException("Collection must not be null");
      }
      Object[] arr = ObjectUtils.toObjectArray(array);
      for (Object elem : arr) {
         collection.add(elem);
      }
   }

   /**
    * Merge the given Properties instance into the given Map,
    * copying all properties (key-value pairs) over.
    * <p>Uses <code>Properties.propertyNames()</code> to even catch
    * default properties linked into the original Properties instance.
    * @param props the Properties instance to merge (may be <code>null</code>)
    * @param map the target Map to merge the properties into
    */
   @SuppressWarnings("unchecked")
   public static void mergePropertiesIntoMap(Properties props, Map map) {
      if (map == null) {
         throw new IllegalArgumentException("Map must not be null");
      }
      if (props != null) {
         for (Enumeration en = props.propertyNames(); en.hasMoreElements();) {
            String key = (String) en.nextElement();
            Object value = props.getProperty(key);
            if (value == null) {
               // Potentially a non-String value...
               value = props.get(key);
            }
            map.put(key, value);
         }
      }
   }


   /**
    * Check whether the given Iterator contains the given element.
    * @param iterator the Iterator to check
    * @param element the element to look for
    * @return <code>true</code> if found, <code>false</code> else
    */
   public static boolean contains(Iterator iterator, Object element) {
      if (iterator != null) {
         while (iterator.hasNext()) {
            Object candidate = iterator.next();
            if (ObjectUtils.nullSafeEquals(candidate, element)) {
               return true;
            }
         }
      }
      return false;
   }

   /**
    * Check whether the given Enumeration contains the given element.
    * @param enumeration the Enumeration to check
    * @param element the element to look for
    * @return <code>true</code> if found, <code>false</code> else
    */
   public static boolean contains(Enumeration enumeration, Object element) {
      if (enumeration != null) {
         while (enumeration.hasMoreElements()) {
            Object candidate = enumeration.nextElement();
            if (ObjectUtils.nullSafeEquals(candidate, element)) {
               return true;
            }
         }
      }
      return false;
   }

   /**
    * Check whether the given Collection contains the given element instance.
    * <p>Enforces the given instance to be present, rather than returning
    * <code>true</code> for an equal element as well.
    * @param collection the Collection to check
    * @param element the element to look for
    * @return <code>true</code> if found, <code>false</code> else
    */
   public static boolean containsInstance(Collection collection, Object element) {
      if (collection != null) {
         for (Object candidate : collection) {
            if (candidate == element) {
               return true;
            }
         }
      }
      return false;
   }

   /**
    * Return <code>true</code> if any element in '<code>candidates</code>' is
    * contained in '<code>source</code>'; otherwise returns <code>false</code>.
    * @param source the source Collection
    * @param candidates the candidates to search for
    * @return whether any of the candidates has been found
    */
   public static boolean containsAny(Collection source, Collection candidates) {
      if (isEmpty(source) || isEmpty(candidates)) {
         return false;
      }
      for (Object candidate : candidates) {
         if (source.contains(candidate)) {
            return true;
         }
      }
      return false;
   }

   /**
    * Return the first element in '<code>candidates</code>' that is contained in
    * '<code>source</code>'. If no element in '<code>candidates</code>' is present in
    * '<code>source</code>' returns <code>null</code>. Iteration order is
    * {@link Collection} implementation specific.
    * @param source the source Collection
    * @param candidates the candidates to search for
    * @return the first present object, or <code>null</code> if not found
    */
   public static Object findFirstMatch(Collection source, Collection candidates) {
      if (isEmpty(source) || isEmpty(candidates)) {
         return null;
      }
      for (Object candidate : candidates) {
         if (source.contains(candidate)) {
            return candidate;
         }
      }
      return null;
   }

   /**
    * Find a single value of the given type in the given Collection.
    * @param collection the Collection to search
    * @param type the type to look for
    * @return a value of the given type found if there is a clear match,
    * or <code>null</code> if none or more than one such value found
    */
   @SuppressWarnings("unchecked")
   public static <T> T findValueOfType(Collection<?> collection, Class<T> type) {
      if (isEmpty(collection)) {
         return null;
      }
      T value = null;
      for (Object element : collection) {
         if (type == null || type.isInstance(element)) {
            if (value != null) {
               // More than one value found... no clear single value.
               return null;
            }
            value = (T) element;
         }
      }
      return value;
   }

   /**
    * Find a single value of one of the given types in the given Collection:
    * searching the Collection for a value of the first type, then
    * searching for a value of the second type, etc.
    * @param collection the collection to search
    * @param types the types to look for, in prioritized order
    * @return a value of one of the given types found if there is a clear match,
    * or <code>null</code> if none or more than one such value found
    */
   public static Object findValueOfType(Collection<?> collection, Class<?>[] types) {
      if (isEmpty(collection) || ObjectUtils.isEmpty(types)) {
         return null;
      }
      for (Class<?> type : types) {
         Object value = findValueOfType(collection, type);
         if (value != null) {
            return value;
         }
      }
      return null;
   }

   /**
    * Determine whether the given Collection only contains a single unique object.
    * @param collection the Collection to check
    * @return <code>true</code> if the collection contains a single reference or
    * multiple references to the same instance, <code>false</code> else
    */
   public static boolean hasUniqueObject(Collection collection) {
      if (isEmpty(collection)) {
         return false;
      }
      boolean hasCandidate = false;
      Object candidate = null;
      for (Object elem : collection) {
         if (!hasCandidate) {
            hasCandidate = true;
            candidate = elem;
         }
         else if (candidate != elem) {
            return false;
         }
      }
      return true;
   }

   /**
    * Find the common element type of the given Collection, if any.
    * @param collection the Collection to check
    * @return the common element type, or <code>null</code> if no clear
    * common type has been found (or the collection was empty)
    */
   public static Class<?> findCommonElementType(Collection collection) {
      if (isEmpty(collection)) {
         return null;
      }
      Class<?> candidate = null;
      for (Object val : collection) {
         if (val != null) {
            if (candidate == null) {
               candidate = val.getClass();
            }
            else if (candidate != val.getClass()) {
               return null;
            }
         }
      }
      return candidate;
   }

   /**
    * Adapts an enumeration to an iterator.
    * @param enumeration the enumeration
    * @return the iterator
    */
   public static <E> Iterator<E> toIterator(Enumeration<E> enumeration) {
      return new EnumerationIterator<E>(enumeration);
   }


   /**
    * Iterator wrapping an Enumeration.
    */
   private static class EnumerationIterator<E> implements Iterator<E> {

      private Enumeration<E> enumeration;

      public EnumerationIterator(Enumeration<E> enumeration) {
         this.enumeration = enumeration;
      }

      public boolean hasNext() {
         return this.enumeration.hasMoreElements();
      }

      public E next() {
         return this.enumeration.nextElement();
      }

      public void remove() throws UnsupportedOperationException {
         throw new UnsupportedOperationException("Not supported");
      }
   }

}
